The present invention related generally to bi-directional flyback converters, and in particular to a regulated bi-directional flyback converter that does not require feedback across an isolation barrier.
DCxe2x80x94DC bi-directional flyback circuits are electrical circuits that can send power from the input of the circuit to the output of the circuit; and from the output back to the input. DCxe2x80x94DC bidirectional flyback converters are used in a variety of applications. For example, dcxe2x80x94dc bidirectional flyback converters have been generally used in power supplies of 100W or less with often multiple outputs.
DCxe2x80x94DC flyback converters typically include a flyback transformer, which is typically a coupled inductor, having a primary winding, and at least one secondary winding. To control the flow of energy across the flyback transformer a solid-state power switch may be used. In conventional circuits, the power switch is often subjected to xe2x80x98hard-switching,xe2x80x99 which is a condition of high-voltage and high current (high power) across the switch during the switching transition times. When the power switches are hard-switched, there are significant, and undesirable power losses.
Because of the problems associated with hard-switching, it is useful to achieve zero-voltage switching (ZVS). As its name implies, ZVS is switching at a substantially zero voltage level across the switch when the switch is turned on. As such, the power across the switch in the flyback circuit is low, and, desirably, the power losses are also low.
DCxe2x80x94DC bi-directional flyback circuits are useful in universal mains voltage power supplies, which allows a device to operate at a variety of ac voltages. It is often desirable to achieve ZVS on the switch on the primary side of a bi-directional flyback circuit for these applications. Unfortunately, in attempting to achieve ZVS by many known techniques, an excessive amount of energy may be recirculated from the output side to the input side; and/or the desired output voltage may not be maintained due to insufficient re-circulated energy. The recirculation of energy in the circuit results in undesirable losses.
To achieve ZVS on the primary side of the bi-directional flyback circuit, it is known to control the peak negative secondary current (and therefore the amount of re-circulated energy). This known approach regulates the output voltage by controlling the xe2x80x98on-timexe2x80x99 of primary side switch using a feedback loop from the output side of the circuit to the input side of the circuit. The feedback loop often incorporates an opto-coupler.
While feedback loops between the primary and secondary sides of a dcxe2x80x94dc bi-directional flyback converter have use in regulating the output voltage and simultaneously achieving the desired ZVS condition without the drawbacks referenced, they add an additional circuit, and an additional level of complexity to the circuit designer.
What is needed, therefore, is a bi-directional flyback circuit that overcomes at least the shortcomings and drawbacks of the circuits and methods described above.
In accordance with an exemplary embodiment of the present invention, a bi-directional flyback circuit includes a primary side switch that regulates the re-circulated energy to achieve substantially zero voltage switching and a secondary-side switch that regulates the output voltage. No feedback circuit between an output side and an input side of the bi-directional flyback circuit is needed for regulating the output voltage.